The present invention relates to a valve for quick release of pneumatic pressure in a pneumatic fluid system. It finds particular application with air brakes used in conjunction with heavy or commercial vehicles and will be described with particular reference thereto. The invention may be used in other applications without departing from the spirit and scope of the invention.
Some air brake valves used in the industry today (e.g., in Europe) do not meet release timing requirements of Federal Motor Vehicle Safety Standard (FMVSS) 121, Air Brake Systems. The release timing requirements relate to how quickly the brakes release after the brake pedal is allowed to return to its normal position. In order to use these valves Brake Systems. The release timing requirements relate to how quickly the brakes release after the brake pedal is allowed to return to its normal position. In order to use these valves in the worldwide market, the release timing must be improved to meet the requirements of this market. As shown in FIG. 1, current brake system valves utilize a fixed inlet orifice 1 to generate a pressure differential across an exhaust diaphragm 2 to enhance the release timing.
When the actuator 3 for the brake valve is released (e.g., foot lifted from a brake pedal), the air flows from the brake chamber 4 to the actuator 3 through a fixed inlet orifice 1. While the fixed inlet orifice does provide some pressure differential across the exhaust diaphragm, relatively little air, less than 50%, actually is exhausted through the exhaust port, and only slight improvements are realized for the release timing. Moreover, this method restricts the inlet capacity of the valve. Furthermore, this method does not sufficiently improve the release timing to meet the FMVSS 121 requirements.
Patent disclosure DE3938101A1 discusses reducing the vent time of a pressure control valve for improved release timing. In this disclosure a “reflux” valve is placed directly in the inlet flow path, thus restricting the inlet flow. Inclusion of a reflux valve that restricts inlet flow doesn't, however, provide both apply and release timing sufficient to meet, for example the requirements of FMVSS 121. Apply timing relates to how quickly the brakes are applied after pressing the brake pedal. The enhancement for the release timing in disclosure DE3938101A1 degrades the performance of the valve for the apply timing. With the current sizing requirements of the antilock brake system (ABS) valve, it is not capable to meet both apply and release timing of FMVSS 121 using the “reflux” valve design.
The present invention provides a new and improved apparatus and method which addresses the above-referenced problems.